Reciprocating Compressor Wrist Pin Bearing and Lubrication Passageway

ABSTRACT

A compressor, as well as a lightweight and strong casting for a compressor, are disclosed. The compressor, which may be a reciprocating compressor for use in compressing high-pressure refrigerants such as CO 2 , includes substantially reduced wall thicknesses (t) compared to prior art castings. The side walls of the compressor can be manufactured to such reduced thicknesses (t) through the use of a bridge spanning across the crankcase. This not only allows the opposing side walls to be manufactured of a thinner material, but the bottom cover removably mounted to the crankcase can be manufactured from a thinner and lighter material as well. Through the use of such a bridge, the resulting compressor is not only able to satisfy current strength requirements, but at significant weight, size and cost savings as well.

CROSS-REFERENCE TO RELATED APPLICATION

This is a non-provisional patent application claiming priority under 35USC §119(e) to U.S. Provisional Patent Application Ser. No. 61/181,929filed on May 28, 2009.

BACKGROUND

1. Technical Field

This disclosure relates to reciprocating compressors and, morespecifically, to reciprocating compressors suitable for use with carbondioxide refrigerant. Still more specifically, this disclosure relates toan improved connecting rod/wrist pin design for more reliable operationof such reciprocating compressors.

2. Description of the Related Art

Compressors are utilized in many applications to compress variousfluids. One type of compressor is a reciprocating piston compressor. Ina reciprocating piston compressor, a crankshaft rotates at least oneeccentric. Each eccentric in turn drives a connecting rod that isconnected to a piston by a wrist pin. The connecting rod typicallyincludes a larger proximal end lined with a bearing that receives theeccentric. The connecting rod also includes a smaller distal end, alsoequipped with a bearing that is typically received on a wrist pin thatconnects the connecting rod to the piston.

A good deal of friction is encountered in these connecting rod bearingsfrom transmitting the force of actuation to the piston. Thus, it isknown in the art to provide lubricant to the various moving surfaces ina compressor to facilitate the movement of the piston and the connectingrod. Typically, a lubricant is driven into a lubricant path inside thecrankshaft where it is distributed to the feedholes for each eccentricand the main bearings. Lubricant may also be communicated up through theconnecting rod to the distal end or wrist pin bearing to lubricate thewrist pin and corresponding bearing in the piston.

In a reciprocating compressor, the wrist pin carries the load forcompressing the gas. The wrist pin has to fit inside the piston so thearea for the bearing surface is limited by the size of the piston borethat receives the wrist pin. Further, the wrist pin requires lubricationto maintain an oil film to reliably carry the load.

In CO₂ compressors, for example, the piston bore is small compared toother compressors so the wrist pin bearing surface area is smallrelative to the high loads required for a CO₂ compressor. The spaceinside the piston is also small which inhibits designs relying uponsplash-feed lubrication to the wrist pin. Because of the problemsassociated with getting lubricant delivered to the wrist pin, thetypical materials such as aluminum for the connecting rod and steel forthe wrist pin are not sufficiently reliable.

U.S. Pat. No. 7,128,528 discloses a two-stage CO₂ compressor and ascroll-type CO₂ compressor that relies upon special materials for itsbearings, such as graphite, but does not address the problems associatedwith stress on wrist pins and delivering lubricant to wrist pins ofreciprocating CO₂ compressors or similar reciprocating compressors. U.S.Publication 2006/0171824 discloses a circuitous lubricant delivery routethrough the central portion of the connecting rod to the wrist pin.However, this design does not permit inclusion of a bearing surroundingthe wrist pin and therefore does not completely address the problem ofpremature wear or failure of a steel wrist pin.

Thus, there is a need for an improved reciprocating compressor wristpin/bearing/connecting rod design that provides reliable lubricantdelivery to the wrist pin and reliable, long-term operation of the wristpin and connecting rod.

SUMMARY OF THE DISCLOSURE

Improved compressors are disclosed that provide better wearcharacteristics for wrist pins and connecting rods of reciprocatingcompressors with small pistons, such as reciprocating compressors forhigher pressure working fluids like CO₂.

One disclosed compressor comprises at least one eccentric and aconnecting rod comprising a proximal end and a distal end. The proximalend of the connecting rod comprises a proximal through opening forming aproximal bearing surface that is connected around the eccentric. Thedistal end of the connecting rod comprises a distal through opening thatforms a distal bearing surface that may be lined with a bearing insertthat may, in turn, be lined with a bearing material that may comprisecarbon, e.g., graphite. The bearing insert is connected around a wristpin. The wrist pin is connected to an interior of the piston. The pistonis movable within a cylinder to compress a working fluid.

The distal end of the connecting rod may further comprise a lubricantpassageway extending through the distal end of the connecting rod andthrough the lined bearing insert to provide fluid communication to thewrist pin. A lubricant supply system may be provided for supplyinglubricant, or splash feeding lubricant, to the interior of the pistonand the wrist pin through the lubricant passageway.

Other advantages and features will be apparent from the followingdetailed description when read in conjunction with the attacheddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the disclosed methods andapparatuses, reference should be made to the embodiments illustrated ingreater detail in the accompanying drawings, wherein:

FIG. 1 is a sectional view of a compressor made in accordance with thisdisclosure;

FIG. 2 is a side sectional view of a connecting rod of the compressorshown in FIG. 1;

FIG. 3 is an exploded view of the connecting rod shown in FIGS. 1-2;

FIG. 4 is an enlarged view of the area labeled 4 of FIG. 1, particularlyillustrating the distal end of the connecting rod, bearing, wrist pinand piston;

FIG. 5 is a partial exploded view of two bearing rods, wrist pins,pistons and seals of the compressor shown in FIG. 1; and

FIG. 6 is an enlarged sectional view of the bearing insert, wrist pinand lubricant passageway.

It should be understood that the drawings are not necessarily to scaleand that the disclosed embodiments are sometimes illustrateddiagrammatically and in partial views. In certain instances, detailswhich are not necessary for an understanding of the disclosed methodsand apparatuses or which render other details difficult to perceive mayhave been omitted. It should be understood, of course, that thisdisclosure is not limited to the particular embodiments illustratedherein.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

A compressor 10 is illustrated in FIG. 1 with a motor (not shown) thatdrives the crankshaft (not shown) that rotates the eccentric 11 receivedwithin the proximal ends 12 of the connecting rod 13. The connecting rod13 includes a distal end 14 that is connected to a piston 15 by a wristpin 16, as best seen in FIGS. 4-5. While only a single connecting rod 13is illustrated in FIG. 1, compressors such as those shown at 10 in FIG.1 typically include four connecting rods 13 or two pairs of connectingrods 13, one such pair of parallel connecting rods 13 being illustratedin FIG. 5. Another connecting rod 13 a is also illustrated in FIG. 1 andis disposed in a parallel relationship with an additional connecting rod13 a (not shown). The connecting rods 13, 13 a may be fabricated fromaluminum, an aluminum alloy, various steels, cast irons or magnesiumalloys.

The pistons 15 shown in FIGS. 1 and 5 move towards and away from thevalve plate 17 and head 18 to compress a gas, such as a refrigerant,while a corresponding pair of pistons (not shown) associated with acorresponding pair of connecting rods 13 a move towards and away fromthe valve plate 17 a and head 18 a.

The compressor 10 includes the casing 21 which, in combination with alubricant supply reservoir shown schematically at 22, provides alubricant distribution network 24 that feeds a lubricant to the requiredareas, such as within each cylinder 23 defined by the casing 21. Onlyone cylinder 23 is shown in FIGS. 1 and 5 but a typical compressor 10will include four cylinders 23. In the embodiment illustrated, thelubricant delivery to the cylinder 23 through various passageways, onlyone of which is shown schematically at 24, is typically referred to as a“splash-feed” system.

Turning to FIGS. 2-3, the connecting rods 13 include a proximal throughopening 26 and a distal through opening 27. The proximal through opening26 provides bearing surfaces 26 a, 26 b for the eccentric 11 but ispreferably lined by a bearing or bearing assembly, such as a pair ofconnecting semi-cylindrical rod bearings 28, 29. In the embodimentillustrated in FIGS. 1-3, the connecting rod 13 is not a unitarystructure but, instead, includes a lower semi-cylindrical portion 31that defines the proximal end 12 and that is connected to the upperportion 32 that defines the distal end 14 and the distal through opening27 of the connecting rod 13. The lower portion 31 may be connected tothe upper portion 32 by a variety of means, such as the fasteningelements 33, locating pins 34 and washers 35 as shown in FIG. 3. Ofcourse, the connecting rods 13, 13 a may also be a unitary structure,depending upon the design of the compressor 10.

FIG. 3 also provides a perspective view of the bearing insert 37disposed within the distal through opening 27 and which receives or isconnected around the wrist pin 16. The bearing insert 37 is preferablyfabricated with a metal backing, such as a steel backing layer, linedwith a carbon containing bearing material, such as a graphite containingbearing material. A sintering layer, such as a bronze sintering layermay be used to adhere the graphite containing later to the steelbacking. The bearing material containing carbon and/or graphite may alsoinclude silica and a resin. The function of the bearing insert 37 is toreduce friction and wear on the wrist pin 16. By employing a bearinginsert 37 lined with a carbon or graphite bearing material for thedistal through opening 27 and wrist pin 16, a lubricant delivery hole oraperture 38 may be provided in the insert 37 to provide lubricantdelivery to the wrist pin 16. FIG. 3 also illustrates a hole or aperture39 passing through the surface 41 of the distal end 14 of the connectingrod 13. As illustrated in FIG. 4, the aligned holes 39, 38 provide alubricant passageway to the wrist pin 16. The hole 38 may be machined ordrilled into the bearing insert 37 initially, or the hole 38 may bemachined/drilled through the insert 37 after the bearing insert 37 ispressed into the distal through opening 27 of the connecting rod 13. Thelatter procedure would, of course, eliminate alignment problems duringassembly. In FIG. 4, the lubricant passageway provided by the holes 39,38 is disposed more or less diametrically opposite the wrist pin 16 fromthe eccentric 11. An alternative lubricant passageway 39 a, 38 a is alsoillustrated in phantom in FIG. 4 which is disposed at an angle θ withrespect to the intersection of line 45 that bisects the wrist pin 16 andeccentric 11 and a central axis 16 a of the wrist pin 16. Thecombination of the hole 38 in the bearing insert 37 and the hole 39 inthe distal end 14 of the connecting rod 13 provides a means fordelivering lubricant to the wrist pin 16 while still providing a bearinginsert 37 for the wrist pin 16. Thus, the design illustrated in FIGS.3-4 provides a unique combination of splash-feed lubricant delivery tothe wrist pin 16 as well as reduced frictional bearing support for thewrist pin 16 in the form of the bearing insert 37.

The bearing insert 37 may be a steel or metal backing lined with acarbon or graphite containing bearing material with an optionalsintering layer disposed between the backing and the carbon or graphitecontaining bearing material. One suitable insert includes a steelbacking, a bronze sintering layer and a graphite resin bearing materiallayer that includes graphite, silica and resin. Such inserts areavailable from Taiho Kogyo Co., Ltd. of Japan.

The lubricant passageway 39, 38 to the wrist pin 16 provided by theholes or apertures 38, 39 enables lubricant to be delivered to the wristpin 16 through a simple splash-feed system illustrated schematically at22, 24 and the directional arrows in FIG. 4. Intricate passagewaysthrough the upper portions 32 of the connecting rods 13 are avoided,thereby reducing the cost of the connecting rods 13. Because lubricantis delivered to the interiors 15 a of the pistons 15 anyway, thelubricant delivery system of the compressor 10 need not be modified toaccommodate the modified connecting rods 13 and bearing inserts 37disclosed herein.

FIG. 5 provides a perspective view of a pair of connecting rods 13 thatillustrates the relative size of the wrist pins 16 and pistons 15. TheO-rings or seals for the pistons are shown at 41, 42.

The working fluid is CO₂. Also, the working fluid may be R410A(http://www51.honeywell.com/sm/410a/index.html) or anotherenvironmentally-friendly refrigerants or working fluids.

FIG. 6 schematically illustrates the flow of lubricant through theopening 38 of the insert to the wrist pin 16 as a result of theoscillating vertical movement of the outer surface 16 b of the wrist pin16 towards and away from the inner surface 37 a of the bearing insert 37as the piston 15 moves up and down during operation of the compressor10. The oil film 49 between the surfaces 16 b, 37 a is formed by thepumping action of the load on the wrist pin 16 in the direction of thearrow 50, which forces oil through the opening 38 in the top 37 b of theinsert 37 towards the bottom 37 c of the insert 37 once per stroke.While not shown in FIG. 6, the inner surface 37 a may be lined with acarbon or graphite containing bearing material with an optionalsintering layer disposed between the backing and the carbon or graphitecontaining bearing material as described above.

INDUSTRIAL APPLICABILITY

Reciprocating compressors 10 are disclosed that provide better wearcharacteristics for wrist pins 16 and connecting rods 13 designed forhigher pressure working fluids like CO₂, R410A and other environmentallyfriendly higher pressure working fluids that will be apparent to thoseskilled in the art. The distal end 14 of the connecting rod 13 comprisesa distal through opening 27 forming a distal bearing surface 27 a linedwith a lined bearing insert 37 that slidably and frictionally receivesthe wrist pin 16. The wrist pin 16 is press-fit into an interior 15 a ofthe piston 15, but the wrist pin 16 can rotate within the bearing insert37. The bearing insert may include a metal backing lined with a carbonor graphite containing bearing material. The piston 15 is movable withina cylinder 23 to compress a working fluid, such as CO₂ or R410A. Otherhigher pressure working fluids will be apparent to those skilled in theart. The lined bearing insert 37 may be combined with a splash-feedlubricant delivery system provided by a hole 39 through the distal end14 of the connecting rod 13 and a corresponding hole 38 through thebearing insert 37. Thus, an improved bearing insert 37 for the wrist pin16 is disclosed. An improved splash-feed lubricant delivery system 22,24, 39 for the wrist pins 16 is also disclosed. Finally, these twodevelopments may be practiced separately or combined in a singleembodiment.

While only certain embodiments have been set forth, alternatives andmodifications will be apparent from the above description to thoseskilled in the art. These and other alternatives are consideredequivalents and within the spirit and scope of this disclosure and theappended claims.

1. A compressor, comprising: a motor; a compression element operativelyassociated with the motor; and a housing surrounding the motor andcompression element, at least one bridge extending between opposing sidewalls of the housing proximate the compression element, the bridge beingintegrally cast with the housing.
 2. The compressor of claim 1, whereinthe housing includes side walls having a maximum wall thickness (t) oftwenty-five millimeters.
 3. The compressor of claim 1, wherein thecompressor further includes a working fluid to be compressed, theworking fluid being a refrigerant.
 4. The compressor of claim 3, whereinthe refrigerant is carbon dioxide.
 5. The compressor of claim 3, whereinthe refrigerant is compressed to an operating pressure of at least 500psi.
 6. The compressor of claim 5, wherein the housing has a burstpressure at least five times the operating pressure.
 7. The compressorof claim 1, wherein the housing (22) includes a crankcase, connectingrods and a drive shaft moving within the crankcase, the bridge extendingacross the crankcase.
 8. The compressor of claim 1, further including abottom cover (66) removable from the crankcase, the bridge extendingacross and in contact with the bottom cover.
 9. The compressor of claim1, wherein the compressor is a reciprocating compressor.
 10. Thecompressor of claim 8, wherein the compression element is a piston. 11.The compressor of claim 1, wherein the housing is made of gray castiron.
 12. The compressor of claim 2, wherein the side walls have a wallthickness (t) of between sixteen and twenty-five millimeters.
 13. Acasting for use with a refrigerant compressor, comprising: a motorcompartment adapted to house a motor; a crankcase compartment integralwith the motor compartment and adapted to house at least one movingcompression element; and a bridge spanning across the crankcasecompartment, the motor compartment, crankcase compartment and bridgebeing cast as one integral piece.
 14. The casting of claim 13, where thecrankcase compartment is closed by a removable cover, the bridgeextending across and in contact with the removable cover when theremovable cover is attached to the casting.
 15. The casting of claim 13,wherein the casting is made of gray cast iron.
 16. The casting of claim13, wherein the refrigerant compressor compresses refrigerant to anoperating pressure, the casting having a burst pressure of at least fivetimes the operating pressure.
 17. The casting of claim 13, wherein thecrankcase compartment includes side walls with a maximum wall thickness(t) of twenty-five millimeters.
 18. The casting of claim 17, wherein theside walls have a thickness (t) between sixteen and twenty-fivemillimeters.